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I also recommend the Wakamatsu station. I also recommend showing up at the station at around 6 AM in time for the Doshu's class. More than likely, a few of the regulars will be arriving at that time as well and offer to guide you. It makes it all so much easier.

Kobayashi Dojo is very famous one. Igarashi dojo is too. I think there's a filipino student in Igarashi dojo. I met him some years ago and he visited Korea with Igarashi sensei. His name may be Louie(?)

As well as the good recommendations from the other posters - it probably would help to get in touch with Aikikai Hombu directly, find out about fees (say what association you're a member of and who's the shihan and sensei in your area).
I think it also wouldn't hurt to show up a day or so before you expect to attend, during the day, so that you can learn more about the administrivia and payments you'll have to take care of before getting in, changing, and getting on the mats with whomever is leading the session...
Cheers,
W